From fb86c85951bca7ea7f7ba03b126ecdeec3e26941 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 15:40:38 -0400
Subject: [PATCH 01/25] convert to typescript

---
 test/unit/{mongo_client.test.js => mongo_client.test.ts} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename test/unit/{mongo_client.test.js => mongo_client.test.ts} (100%)

diff --git a/test/unit/mongo_client.test.js b/test/unit/mongo_client.test.ts
similarity index 100%
rename from test/unit/mongo_client.test.js
rename to test/unit/mongo_client.test.ts

From 042e9aa385da9d0ee8ea668021e2827185134c60 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 15:45:05 -0400
Subject: [PATCH 02/25] small fixes

---
 test/unit/mongo_client.test.ts | 45 ++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 21 deletions(-)

diff --git a/test/unit/mongo_client.test.ts b/test/unit/mongo_client.test.ts
index e3b3beb92b..f302d48efb 100644
--- a/test/unit/mongo_client.test.ts
+++ b/test/unit/mongo_client.test.ts
@@ -1,28 +1,28 @@
-('use strict');
-
+import { expect } from 'chai';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as sinon from 'sinon';
+import { Writable } from 'stream';
 import { inspect } from 'util';
 
-const os = require('os');
-const fs = require('fs');
-const { expect } = require('chai');
-const { getSymbolFrom } = require('../tools/utils');
-const { parseOptions, resolveSRVRecord } = require('../mongodb');
-const { ReadConcern } = require('../mongodb');
-const { WriteConcern } = require('../mongodb');
-const { ReadPreference } = require('../mongodb');
-const { MongoCredentials } = require('../mongodb');
-const {
+import {
+  MongoAPIError,
   MongoClient,
+  type MongoClientOptions,
+  MongoCredentials,
+  MongoInvalidArgumentError,
+  MongoLoggableComponent,
+  MongoLogger,
   MongoParseError,
+  parseOptions,
+  ReadConcern,
+  ReadPreference,
+  resolveSRVRecord,
   ServerApiVersion,
-  MongoAPIError,
-  MongoInvalidArgumentError
-} = require('../mongodb');
-const { MongoLogger } = require('../mongodb');
-// eslint-disable-next-line no-restricted-modules
-const { SeverityLevel, MongoLoggableComponent } = require('../../src/mongo_logger');
-const sinon = require('sinon');
-const { Writable } = require('stream');
+  SeverityLevel,
+  WriteConcern
+} from '../mongodb';
+import { getSymbolFrom } from '../tools/utils';
 
 describe('MongoClient', function () {
   it('MongoClient should always freeze public options', function () {
@@ -144,7 +144,10 @@ describe('MongoClient', function () {
   };
 
   it('should parse all options from the options object', function () {
-    const options = parseOptions('mongodb://localhost:27017/', ALL_OPTIONS);
+    const options = parseOptions(
+      'mongodb://localhost:27017/',
+      ALL_OPTIONS as unknown as MongoClientOptions
+    );
     // Check consolidated options
     expect(options).has.property('writeConcern');
     expect(options.writeConcern).has.property('w', 2);

From 2ac89dc28f61b8a89f3b697ba5a65a3929e91368 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:06:15 -0400
Subject: [PATCH 03/25] add option parsing tests

---
 test/unit/connection_string.test.ts | 104 ++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)

diff --git a/test/unit/connection_string.test.ts b/test/unit/connection_string.test.ts
index 2a38fc491a..617ca41c8c 100644
--- a/test/unit/connection_string.test.ts
+++ b/test/unit/connection_string.test.ts
@@ -14,8 +14,10 @@ import {
   DOCUMENT_DB_MSG,
   FEATURE_FLAGS,
   type Log,
+  Long,
   MongoAPIError,
   MongoClient,
+  type MongoClientOptions,
   MongoCredentials,
   MongoDriverError,
   MongoInvalidArgumentError,
@@ -922,6 +924,108 @@ describe('Connection String', function () {
     });
   });
 
+  describe('when timeoutMS is provided as a client option', function () {
+    const connString = 'mongodb://host';
+    const types = ['number', 'bigint', 'Long'];
+    const values = [-100, 0, 100];
+
+    for (const type of types) {
+      describe(`when timeoutMS provided as a ${type}`, function () {
+        for (const v of values) {
+          const timeoutMS =
+            type === 'number' ? v : type === 'bigint' ? BigInt(v) : Long.fromNumber(v);
+          describe(`when timeoutMS is ${
+            v < 0 ? 'negative' : v > 0 ? 'positive' : 'zero'
+          }`, function () {
+            if (v >= 0) {
+              it('sets the value correctly as a number', function () {
+                const options = parseOptions(connString, { timeoutMS });
+                expect(options.timeoutMS).to.equal(v);
+              });
+            } else {
+              it('throws MongoParseError', function () {
+                expect(() => parseOptions(connString, { timeoutMS })).to.throw(MongoParseError);
+              });
+            }
+          });
+        }
+      });
+    }
+  });
+
+  describe('when defaultTimeoutMS is provided as a client option', function () {
+    const connString = 'mongodb://host';
+    const types = ['number', 'bigint', 'Long'];
+    const values = [-100, 0, 100];
+
+    for (const type of types) {
+      describe(`when timeoutMS provided as a ${type}`, function () {
+        for (const v of values) {
+          const defaultTimeoutMS =
+            type === 'number' ? v : type === 'bigint' ? BigInt(v) : Long.fromNumber(v);
+          describe(`when timeoutMS is ${
+            v < 0 ? 'negative' : v > 0 ? 'positive' : 'zero'
+          }`, function () {
+            if (v >= 0) {
+              it('sets the value correctly as a number', function () {
+                const options = parseOptions(connString, { defaultTimeoutMS });
+                expect(options.defaultTimeoutMS).to.equal(v);
+              });
+            } else {
+              it('throws MongoParseError', function () {
+                expect(() => parseOptions(connString, { defaultTimeoutMS })).to.throw(
+                  MongoParseError
+                );
+              });
+            }
+          });
+        }
+      });
+    }
+  });
+
+  describe('when timeoutMS is provided in the connection string', function () {
+    const values = [-100, 0, 100];
+    for (const v of values) {
+      const connString = `mongodb://host?timeoutMS=${v}`;
+      describe(`when timeoutMS is ${
+        v < 0 ? 'negative' : v > 0 ? 'positive' : 'zero'
+      }`, function () {
+        if (v >= 0) {
+          it('sets the value correctly as a number', function () {
+            const options = parseOptions(connString);
+            expect(options.timeoutMS).to.equal(v);
+          });
+        } else {
+          it('throws MongoParseError', function () {
+            expect(() => parseOptions(connString)).to.throw(MongoParseError);
+          });
+        }
+      });
+    }
+  });
+
+  describe('when defaultTimeoutMS is provided in the connection string', function () {
+    const values = [-100, 0, 100];
+    for (const v of values) {
+      const connString = `mongodb://host?defaultTimeoutMS=${v}`;
+      describe(`when defaultTimeoutMS is ${
+        v < 0 ? 'negative' : v > 0 ? 'positive' : 'zero'
+      }`, function () {
+        if (v >= 0) {
+          it('sets the value correctly as a number', function () {
+            const options = parseOptions(connString);
+            expect(options.defaultTimeoutMS).to.equal(v);
+          });
+        } else {
+          it('throws MongoParseError', function () {
+            expect(() => parseOptions(connString)).to.throw(MongoParseError);
+          });
+        }
+      });
+    }
+  });
+
   describe('non-genuine hosts', () => {
     beforeEach(() => {
       process.env.MONGODB_LOG_CLIENT = 'info';

From 06622697ff726398f9e934850d3c0e7597f8293a Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:18:40 -0400
Subject: [PATCH 04/25] add client tests

---
 test/unit/mongo_client.test.ts | 48 ++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/test/unit/mongo_client.test.ts b/test/unit/mongo_client.test.ts
index f302d48efb..8e56b897ff 100644
--- a/test/unit/mongo_client.test.ts
+++ b/test/unit/mongo_client.test.ts
@@ -1208,4 +1208,52 @@ describe('MongoClient', function () {
       expect.fail('missed exception');
     });
   });
+
+  context('timeoutMS', function () {
+    context('when timeoutMS is negative', function () {
+      it('throws MongoParseError', function () {
+        expect(() => new MongoClient('mongodb://host', { timeoutMS: -1 })).to.throw(
+          MongoParseError
+        );
+      });
+    });
+
+    context('when timeoutMS is positive', function () {
+      it('sets the value on the MongoClient', function () {
+        const client = new MongoClient('mongodb://host', { timeoutMS: 1 });
+        expect(client.options.timeoutMS).to.equal(1);
+      });
+    });
+
+    context('when timeoutMS is zero', function () {
+      it('sets the value on the MongoClient', function () {
+        const client = new MongoClient('mongodb://host', { timeoutMS: 0 });
+        expect(client.options.timeoutMS).to.equal(0);
+      });
+    });
+  });
+
+  context('defaultTimeoutMS', function () {
+    context('when defaultTimeoutMS is negative', function () {
+      it('throws MongoParseError', function () {
+        expect(() => new MongoClient('mongodb://host', { defaultTimeoutMS: -1 })).to.throw(
+          MongoParseError
+        );
+      });
+    });
+
+    context('when defaultTimeoutMS is positive', function () {
+      it('sets the value on the MongoClient', function () {
+        const client = new MongoClient('mongodb://host', { defaultTimeoutMS: 1 });
+        expect(client.options.defaultTimeoutMS).to.equal(1);
+      });
+    });
+
+    context('when defaultTimeoutMS is zero', function () {
+      it('sets the value on the MongoClient', function () {
+        const client = new MongoClient('mongodb://host', { defaultTimeoutMS: 0 });
+        expect(client.options.defaultTimeoutMS).to.equal(0);
+      });
+    });
+  });
 });

From cd562ca73aa1b2f9d3b4cfc222065a8e254b4aac Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:20:26 -0400
Subject: [PATCH 05/25] add client and connection string support for
 defaultTimeoutMS

---
 src/connection_string.ts | 3 +++
 src/mongo_client.ts      | 8 ++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/connection_string.ts b/src/connection_string.ts
index c2abf08aaa..c22f54444b 100644
--- a/src/connection_string.ts
+++ b/src/connection_string.ts
@@ -1108,6 +1108,9 @@ export const OPTIONS = {
   timeoutMS: {
     type: 'uint'
   },
+  defaultTimeoutMS: {
+    type: 'uint'
+  },
   tls: {
     type: 'boolean'
   },
diff --git a/src/mongo_client.ts b/src/mongo_client.ts
index 98a9f151ac..61dfeb35ee 100644
--- a/src/mongo_client.ts
+++ b/src/mongo_client.ts
@@ -2,7 +2,7 @@ import { promises as fs } from 'fs';
 import type { TcpNetConnectOpts } from 'net';
 import type { ConnectionOptions as TLSConnectionOptions, TLSSocketOptions } from 'tls';
 
-import { type BSONSerializeOptions, type Document, resolveBSONOptions } from './bson';
+import { type BSONSerializeOptions, type Document, type Long, resolveBSONOptions } from './bson';
 import { ChangeStream, type ChangeStreamDocument, type ChangeStreamOptions } from './change_stream';
 import type { AutoEncrypter, AutoEncryptionOptions } from './client-side-encryption/auto_encrypter';
 import {
@@ -121,7 +121,9 @@ export interface MongoClientOptions extends BSONSerializeOptions, SupportedNodeC
   /** Specifies the name of the replica set, if the mongod is a member of a replica set. */
   replicaSet?: string;
   /** @internal This option is in development and currently has no behaviour. */
-  timeoutMS?: number;
+  timeoutMS?: number | bigint | Long;
+  /** @internal This option is in development and currently has no behaviour. */
+  defaultTimeoutMS?: number | bigint | Long;
   /** Enables or disables TLS/SSL for the connection. */
   tls?: boolean;
   /** A boolean to enable or disables TLS/SSL for the connection. (The ssl option is equivalent to the tls option.) */
@@ -803,6 +805,8 @@ export interface MongoOptions
         | 'socketTimeoutMS'
         | 'srvMaxHosts'
         | 'srvServiceName'
+        | 'timeoutMS'
+        | 'defaultTimeoutMS'
         | 'tlsAllowInvalidCertificates'
         | 'tlsAllowInvalidHostnames'
         | 'tlsInsecure'

From 79230291b5d120bf8aa1a649d13f9914a90fc2cf Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:50:24 -0400
Subject: [PATCH 06/25] lint fix

---
 test/unit/connection_string.test.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/test/unit/connection_string.test.ts b/test/unit/connection_string.test.ts
index 617ca41c8c..4d46f0802a 100644
--- a/test/unit/connection_string.test.ts
+++ b/test/unit/connection_string.test.ts
@@ -17,7 +17,6 @@ import {
   Long,
   MongoAPIError,
   MongoClient,
-  type MongoClientOptions,
   MongoCredentials,
   MongoDriverError,
   MongoInvalidArgumentError,

From 07b57a0d34ce3cebd802f1e2ec08b7b8a2bb3e42 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:51:11 -0400
Subject: [PATCH 07/25] Add support for timeoutMS and defaultTimeoutMS to db

---
 src/db.ts | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/db.ts b/src/db.ts
index 1dda4834c2..c52d979eef 100644
--- a/src/db.ts
+++ b/src/db.ts
@@ -7,7 +7,7 @@ import { AggregationCursor } from './cursor/aggregation_cursor';
 import { ListCollectionsCursor } from './cursor/list_collections_cursor';
 import { RunCommandCursor, type RunCursorCommandOptions } from './cursor/run_command_cursor';
 import { MongoInvalidArgumentError } from './error';
-import type { MongoClient, PkFactory } from './mongo_client';
+import type { MongoClient, MongoClientOptions, PkFactory } from './mongo_client';
 import type { TODO_NODE_3286 } from './mongo_types';
 import type { AggregateOptions } from './operations/aggregate';
 import { CollectionsOperation } from './operations/collections';
@@ -66,7 +66,9 @@ const DB_OPTIONS_ALLOW_LIST = [
   'enableUtf8Validation',
   'promoteValues',
   'compression',
-  'retryWrites'
+  'retryWrites',
+  'timeoutMS',
+  'defaultTimeoutMS'
 ];
 
 /** @internal */
@@ -81,7 +83,10 @@ export interface DbPrivate {
 }
 
 /** @public */
-export interface DbOptions extends BSONSerializeOptions, WriteConcernOptions {
+export interface DbOptions
+  extends BSONSerializeOptions,
+    WriteConcernOptions,
+    Pick<MongoClientOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
   /** If the database authentication is dependent on another databaseName. */
   authSource?: string;
   /** Force server to assign _id values instead of driver. */

From 4c8219e8f98cd11238dac22b68df9f893e97509f Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:55:36 -0400
Subject: [PATCH 08/25] Add support for timeoutMS and defaultTimeoutMS to
 collection

---
 src/collection.ts | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/collection.ts b/src/collection.ts
index 8fcdf90bff..b481129393 100644
--- a/src/collection.ts
+++ b/src/collection.ts
@@ -10,7 +10,7 @@ import {
   ListSearchIndexesCursor,
   type ListSearchIndexesOptions
 } from './cursor/list_search_indexes_cursor';
-import type { Db } from './db';
+import type { Db, DbOptions } from './db';
 import { MongoInvalidArgumentError } from './error';
 import type { MongoClient, PkFactory } from './mongo_client';
 import type {
@@ -101,7 +101,10 @@ export interface ModifyResult<TSchema = Document> {
 }
 
 /** @public */
-export interface CollectionOptions extends BSONSerializeOptions, WriteConcernOptions {
+export interface CollectionOptions
+  extends BSONSerializeOptions,
+    WriteConcernOptions,
+    Pick<DbOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
   /** Specify a read concern for the collection. (only MongoDB 3.2 or higher supported) */
   readConcern?: ReadConcernLike;
   /** The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST). */

From e3a1548703e947a9bf82ef9e1386b99c55f55f0f Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:56:17 -0400
Subject: [PATCH 09/25] Add support for timeoutMS and defaultTimeoutMS to
 gridfs

---
 src/gridfs/download.ts | 4 +++-
 src/gridfs/index.ts    | 5 ++++-
 src/gridfs/upload.ts   | 6 ++++--
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/gridfs/download.ts b/src/gridfs/download.ts
index 08659dfabf..8e8ca673f6 100644
--- a/src/gridfs/download.ts
+++ b/src/gridfs/download.ts
@@ -13,10 +13,12 @@ import type { FindOptions } from '../operations/find';
 import type { ReadPreference } from '../read_preference';
 import type { Sort } from '../sort';
 import type { Callback } from '../utils';
+import { type GridFSBucketOptions } from '.';
 import type { GridFSChunk } from './upload';
 
 /** @public */
-export interface GridFSBucketReadStreamOptions {
+export interface GridFSBucketReadStreamOptions
+  extends Pick<GridFSBucketOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
   sort?: Sort;
   skip?: number;
   /**
diff --git a/src/gridfs/index.ts b/src/gridfs/index.ts
index c7611c852b..95cf43db55 100644
--- a/src/gridfs/index.ts
+++ b/src/gridfs/index.ts
@@ -3,6 +3,7 @@ import type { Collection } from '../collection';
 import type { FindCursor } from '../cursor/find_cursor';
 import type { Db } from '../db';
 import { MongoRuntimeError } from '../error';
+import { type MongoClientOptions } from '../mongo_client';
 import { type Filter, TypedEventEmitter } from '../mongo_types';
 import type { ReadPreference } from '../read_preference';
 import type { Sort } from '../sort';
@@ -29,7 +30,9 @@ const DEFAULT_GRIDFS_BUCKET_OPTIONS: {
 };
 
 /** @public */
-export interface GridFSBucketOptions extends WriteConcernOptions {
+export interface GridFSBucketOptions
+  extends WriteConcernOptions,
+    Pick<MongoClientOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
   /** The 'files' and 'chunks' collections will be prefixed with the bucket name followed by a dot. */
   bucketName?: string;
   /** Number of bytes stored in each chunk. Defaults to 255KB */
diff --git a/src/gridfs/upload.ts b/src/gridfs/upload.ts
index 80024d7d32..9c013bfd0b 100644
--- a/src/gridfs/upload.ts
+++ b/src/gridfs/upload.ts
@@ -8,7 +8,7 @@ import { type Callback, squashError } from '../utils';
 import type { WriteConcernOptions } from '../write_concern';
 import { WriteConcern } from './../write_concern';
 import type { GridFSFile } from './download';
-import type { GridFSBucket } from './index';
+import type { GridFSBucket, GridFSBucketOptions } from './index';
 
 /** @public */
 export interface GridFSChunk {
@@ -19,7 +19,9 @@ export interface GridFSChunk {
 }
 
 /** @public */
-export interface GridFSBucketWriteStreamOptions extends WriteConcernOptions {
+export interface GridFSBucketWriteStreamOptions
+  extends WriteConcernOptions,
+    Pick<GridFSBucketOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
   /** Overwrite this bucket's chunkSizeBytes for this file */
   chunkSizeBytes?: number;
   /** Custom file id for the GridFS file. */

From 504eba729b8b0873e4f79c310cb3ab54fe63433c Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:57:20 -0400
Subject: [PATCH 10/25] Add support for timeoutMS and defaultTimeoutMS to
 operations

---
 src/operations/operation.ts | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/operations/operation.ts b/src/operations/operation.ts
index 7f564cbc27..fb31665097 100644
--- a/src/operations/operation.ts
+++ b/src/operations/operation.ts
@@ -1,4 +1,5 @@
 import { type BSONSerializeOptions, type Document, resolveBSONOptions } from '../bson';
+import { type MongoClientOptions } from '../mongo_client';
 import { ReadPreference, type ReadPreferenceLike } from '../read_preference';
 import type { Server } from '../sdam/server';
 import type { ClientSession } from '../sessions';
@@ -23,7 +24,9 @@ export interface OperationConstructor extends Function {
 }
 
 /** @public */
-export interface OperationOptions extends BSONSerializeOptions {
+export interface OperationOptions
+  extends BSONSerializeOptions,
+    Pick<MongoClientOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
   /** Specify ClientSession for this command */
   session?: ClientSession;
   willRetryWrite?: boolean;

From dc1aaf4e98db8b3ebdbdcd0bfa82c3821838ec67 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Wed, 3 Apr 2024 16:57:44 -0400
Subject: [PATCH 11/25] Add support for timeoutMS and defaultTimeoutMS to
 sessions

---
 src/sessions.ts | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/sessions.ts b/src/sessions.ts
index 8f2892f0c0..6c4e82b203 100644
--- a/src/sessions.ts
+++ b/src/sessions.ts
@@ -23,7 +23,7 @@ import {
   MongoTransactionError,
   MongoWriteConcernError
 } from './error';
-import type { MongoClient, MongoOptions } from './mongo_client';
+import type { MongoClient, MongoClientOptions, MongoOptions } from './mongo_client';
 import { TypedEventEmitter } from './mongo_types';
 import { executeOperation } from './operations/execute_operation';
 import { RunAdminCommandOperation } from './operations/run_command';
@@ -53,7 +53,8 @@ import { WriteConcern } from './write_concern';
 const minWireVersionForShardedTransactions = 8;
 
 /** @public */
-export interface ClientSessionOptions {
+export interface ClientSessionOptions
+  extends Pick<MongoClientOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
   /** Whether causal consistency should be enabled on this session */
   causalConsistency?: boolean;
   /** Whether all read operations should be read from the same snapshot for this session (NOTE: not compatible with `causalConsistency=true`) */

From 7142a0d1d63659b1de8bd07db2e7056e21d173bd Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Thu, 4 Apr 2024 16:40:30 -0400
Subject: [PATCH 12/25] pull in uri spec tests

---
 test/spec/uri-options/connection-options.json | 34 +++++++++++++++++--
 test/spec/uri-options/connection-options.yml  | 30 ++++++++++++++--
 .../uri-options/connection-pool-options.yml   |  1 -
 .../uri-options/read-preference-options.json  |  2 +-
 .../uri-options/read-preference-options.yml   |  2 +-
 5 files changed, 62 insertions(+), 7 deletions(-)

diff --git a/test/spec/uri-options/connection-options.json b/test/spec/uri-options/connection-options.json
index 8bb05cc721..b2669b6cf1 100644
--- a/test/spec/uri-options/connection-options.json
+++ b/test/spec/uri-options/connection-options.json
@@ -2,7 +2,7 @@
   "tests": [
     {
       "description": "Valid connection and timeout options are parsed correctly",
-      "uri": "mongodb://example.com/?appname=URI-OPTIONS-SPEC-TEST&connectTimeoutMS=20000&heartbeatFrequencyMS=5000&localThresholdMS=3000&maxIdleTimeMS=50000&replicaSet=uri-options-spec&retryWrites=true&serverSelectionTimeoutMS=15000&socketTimeoutMS=7500",
+      "uri": "mongodb://example.com/?appname=URI-OPTIONS-SPEC-TEST&connectTimeoutMS=20000&heartbeatFrequencyMS=5000&localThresholdMS=3000&maxIdleTimeMS=50000&replicaSet=uri-options-spec&retryWrites=true&serverSelectionTimeoutMS=15000&socketTimeoutMS=7500&timeoutMS=100",
       "valid": true,
       "warning": false,
       "hosts": null,
@@ -16,7 +16,8 @@
         "replicaSet": "uri-options-spec",
         "retryWrites": true,
         "serverSelectionTimeoutMS": 15000,
-        "socketTimeoutMS": 7500
+        "socketTimeoutMS": 7500,
+        "timeoutMS": 100
       }
     },
     {
@@ -238,6 +239,35 @@
       "hosts": null,
       "auth": null,
       "options": {}
+    },
+    {
+      "description": "timeoutMS=0",
+      "uri": "mongodb://example.com/?timeoutMS=0",
+      "valid": true,
+      "warning": false,
+      "hosts": null,
+      "auth": null,
+      "options": {
+        "timeoutMS": 0
+      }
+    },
+    {
+      "description": "Non-numeric timeoutMS causes a warning",
+      "uri": "mongodb://example.com/?timeoutMS=invalid",
+      "valid": true,
+      "warning": true,
+      "hosts": null,
+      "auth": null,
+      "options": {}
+    },
+    {
+      "description": "Too low timeoutMS causes a warning",
+      "uri": "mongodb://example.com/?timeoutMS=-2",
+      "valid": true,
+      "warning": true,
+      "hosts": null,
+      "auth": null,
+      "options": {}
     }
   ]
 }
diff --git a/test/spec/uri-options/connection-options.yml b/test/spec/uri-options/connection-options.yml
index 83f63daa1a..43ef9ec9b3 100644
--- a/test/spec/uri-options/connection-options.yml
+++ b/test/spec/uri-options/connection-options.yml
@@ -1,7 +1,7 @@
 tests:
     -
         description: "Valid connection and timeout options are parsed correctly"
-        uri: "mongodb://example.com/?appname=URI-OPTIONS-SPEC-TEST&connectTimeoutMS=20000&heartbeatFrequencyMS=5000&localThresholdMS=3000&maxIdleTimeMS=50000&replicaSet=uri-options-spec&retryWrites=true&serverSelectionTimeoutMS=15000&socketTimeoutMS=7500"
+        uri: "mongodb://example.com/?appname=URI-OPTIONS-SPEC-TEST&connectTimeoutMS=20000&heartbeatFrequencyMS=5000&localThresholdMS=3000&maxIdleTimeMS=50000&replicaSet=uri-options-spec&retryWrites=true&serverSelectionTimeoutMS=15000&socketTimeoutMS=7500&timeoutMS=100"
         valid: true
         warning: false
         hosts: ~
@@ -16,6 +16,7 @@ tests:
             retryWrites: true
             serverSelectionTimeoutMS: 15000
             socketTimeoutMS: 7500
+            timeoutMS: 100
     -
         description: "Non-numeric connectTimeoutMS causes a warning"
         uri: "mongodb://example.com/?connectTimeoutMS=invalid"
@@ -64,7 +65,7 @@ tests:
         hosts: ~
         auth: ~
         options: {}
-    -
+    - 
         description: "Invalid retryWrites causes a warning"
         uri: "mongodb://example.com/?retryWrites=invalid"
         valid: true
@@ -207,3 +208,28 @@ tests:
       hosts: ~
       auth: ~
       options: {}
+    -
+        description: "timeoutMS=0"
+        uri: "mongodb://example.com/?timeoutMS=0"
+        valid: true
+        warning: false
+        hosts: ~
+        auth: ~
+        options:
+            timeoutMS: 0
+    -
+        description: "Non-numeric timeoutMS causes a warning"
+        uri: "mongodb://example.com/?timeoutMS=invalid"
+        valid: true
+        warning: true
+        hosts: ~
+        auth: ~
+        options: {}
+    -
+        description: "Too low timeoutMS causes a warning"
+        uri: "mongodb://example.com/?timeoutMS=-2"
+        valid: true
+        warning: true
+        hosts: ~
+        auth: ~
+        options: {}
diff --git a/test/spec/uri-options/connection-pool-options.yml b/test/spec/uri-options/connection-pool-options.yml
index 65fbb7367c..0333d4e31e 100644
--- a/test/spec/uri-options/connection-pool-options.yml
+++ b/test/spec/uri-options/connection-pool-options.yml
@@ -65,4 +65,3 @@ tests:
       hosts: ~
       auth: ~
       options: {}
-      
\ No newline at end of file
diff --git a/test/spec/uri-options/read-preference-options.json b/test/spec/uri-options/read-preference-options.json
index df8c0c0eb8..cdac6a63c3 100644
--- a/test/spec/uri-options/read-preference-options.json
+++ b/test/spec/uri-options/read-preference-options.json
@@ -23,7 +23,7 @@
     },
     {
       "description": "Single readPreferenceTags is parsed as array of size one",
-      "uri": "mongodb://example.com/?readPreferenceTags=dc:ny",
+      "uri": "mongodb://example.com/?readPreference=secondary&readPreferenceTags=dc:ny",
       "valid": true,
       "warning": false,
       "hosts": null,
diff --git a/test/spec/uri-options/read-preference-options.yml b/test/spec/uri-options/read-preference-options.yml
index cac8c6d89c..4ced669acf 100644
--- a/test/spec/uri-options/read-preference-options.yml
+++ b/test/spec/uri-options/read-preference-options.yml
@@ -17,7 +17,7 @@ tests:
             maxStalenessSeconds: 120
     -
         description: "Single readPreferenceTags is parsed as array of size one"
-        uri: "mongodb://example.com/?readPreferenceTags=dc:ny"
+        uri: "mongodb://example.com/?readPreference=secondary&readPreferenceTags=dc:ny"
         valid: true
         warning: false
         hosts: ~

From 75acc7b508f27038187855c1173e61169128b6bc Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Thu, 4 Apr 2024 16:41:04 -0400
Subject: [PATCH 13/25] support timeoutMS option on uri-spec-runner

---
 test/tools/uri_spec_runner.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/tools/uri_spec_runner.ts b/test/tools/uri_spec_runner.ts
index 6ad6e86381..844e5bd470 100644
--- a/test/tools/uri_spec_runner.ts
+++ b/test/tools/uri_spec_runner.ts
@@ -349,6 +349,7 @@ export function executeUriValidationTest(
       case 'maxConnecting':
       case 'maxPoolSize':
       case 'minPoolSize':
+      case 'timeoutMS':
       case 'connectTimeoutMS':
       case 'heartbeatFrequencyMS':
       case 'localThresholdMS':

From 524ccf9580ba4ef7b70ffa5c29ece65bc033c7a3 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Thu, 4 Apr 2024 16:41:38 -0400
Subject: [PATCH 14/25] remove defaultTimeoutMS option

---
 test/unit/connection_string.test.ts | 52 -----------------------------
 test/unit/mongo_client.test.ts      | 24 -------------
 2 files changed, 76 deletions(-)

diff --git a/test/unit/connection_string.test.ts b/test/unit/connection_string.test.ts
index 4d46f0802a..ab4b827d7a 100644
--- a/test/unit/connection_string.test.ts
+++ b/test/unit/connection_string.test.ts
@@ -952,37 +952,6 @@ describe('Connection String', function () {
     }
   });
 
-  describe('when defaultTimeoutMS is provided as a client option', function () {
-    const connString = 'mongodb://host';
-    const types = ['number', 'bigint', 'Long'];
-    const values = [-100, 0, 100];
-
-    for (const type of types) {
-      describe(`when timeoutMS provided as a ${type}`, function () {
-        for (const v of values) {
-          const defaultTimeoutMS =
-            type === 'number' ? v : type === 'bigint' ? BigInt(v) : Long.fromNumber(v);
-          describe(`when timeoutMS is ${
-            v < 0 ? 'negative' : v > 0 ? 'positive' : 'zero'
-          }`, function () {
-            if (v >= 0) {
-              it('sets the value correctly as a number', function () {
-                const options = parseOptions(connString, { defaultTimeoutMS });
-                expect(options.defaultTimeoutMS).to.equal(v);
-              });
-            } else {
-              it('throws MongoParseError', function () {
-                expect(() => parseOptions(connString, { defaultTimeoutMS })).to.throw(
-                  MongoParseError
-                );
-              });
-            }
-          });
-        }
-      });
-    }
-  });
-
   describe('when timeoutMS is provided in the connection string', function () {
     const values = [-100, 0, 100];
     for (const v of values) {
@@ -1004,27 +973,6 @@ describe('Connection String', function () {
     }
   });
 
-  describe('when defaultTimeoutMS is provided in the connection string', function () {
-    const values = [-100, 0, 100];
-    for (const v of values) {
-      const connString = `mongodb://host?defaultTimeoutMS=${v}`;
-      describe(`when defaultTimeoutMS is ${
-        v < 0 ? 'negative' : v > 0 ? 'positive' : 'zero'
-      }`, function () {
-        if (v >= 0) {
-          it('sets the value correctly as a number', function () {
-            const options = parseOptions(connString);
-            expect(options.defaultTimeoutMS).to.equal(v);
-          });
-        } else {
-          it('throws MongoParseError', function () {
-            expect(() => parseOptions(connString)).to.throw(MongoParseError);
-          });
-        }
-      });
-    }
-  });
-
   describe('non-genuine hosts', () => {
     beforeEach(() => {
       process.env.MONGODB_LOG_CLIENT = 'info';
diff --git a/test/unit/mongo_client.test.ts b/test/unit/mongo_client.test.ts
index 8e56b897ff..79663a2603 100644
--- a/test/unit/mongo_client.test.ts
+++ b/test/unit/mongo_client.test.ts
@@ -1232,28 +1232,4 @@ describe('MongoClient', function () {
       });
     });
   });
-
-  context('defaultTimeoutMS', function () {
-    context('when defaultTimeoutMS is negative', function () {
-      it('throws MongoParseError', function () {
-        expect(() => new MongoClient('mongodb://host', { defaultTimeoutMS: -1 })).to.throw(
-          MongoParseError
-        );
-      });
-    });
-
-    context('when defaultTimeoutMS is positive', function () {
-      it('sets the value on the MongoClient', function () {
-        const client = new MongoClient('mongodb://host', { defaultTimeoutMS: 1 });
-        expect(client.options.defaultTimeoutMS).to.equal(1);
-      });
-    });
-
-    context('when defaultTimeoutMS is zero', function () {
-      it('sets the value on the MongoClient', function () {
-        const client = new MongoClient('mongodb://host', { defaultTimeoutMS: 0 });
-        expect(client.options.defaultTimeoutMS).to.equal(0);
-      });
-    });
-  });
 });

From 51724dbc520d8eed9d33ea103da260fe5bee79c9 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Thu, 4 Apr 2024 17:01:23 -0400
Subject: [PATCH 15/25] fix option implementation

---
 src/collection.ts           |  9 ++++-----
 src/connection_string.ts    |  3 ---
 src/db.ts                   | 12 +++++-------
 src/gridfs/download.ts      |  6 +++---
 src/gridfs/index.ts         |  7 +++----
 src/gridfs/upload.ts        |  8 ++++----
 src/mongo_client.ts         | 10 ++++------
 src/operations/operation.ts |  8 ++++----
 src/sessions.ts             | 12 +++++++++---
 9 files changed, 36 insertions(+), 39 deletions(-)

diff --git a/src/collection.ts b/src/collection.ts
index b481129393..180e9822e8 100644
--- a/src/collection.ts
+++ b/src/collection.ts
@@ -10,7 +10,7 @@ import {
   ListSearchIndexesCursor,
   type ListSearchIndexesOptions
 } from './cursor/list_search_indexes_cursor';
-import type { Db, DbOptions } from './db';
+import type { Db } from './db';
 import { MongoInvalidArgumentError } from './error';
 import type { MongoClient, PkFactory } from './mongo_client';
 import type {
@@ -101,14 +101,13 @@ export interface ModifyResult<TSchema = Document> {
 }
 
 /** @public */
-export interface CollectionOptions
-  extends BSONSerializeOptions,
-    WriteConcernOptions,
-    Pick<DbOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
+export interface CollectionOptions extends BSONSerializeOptions, WriteConcernOptions {
   /** Specify a read concern for the collection. (only MongoDB 3.2 or higher supported) */
   readConcern?: ReadConcernLike;
   /** The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST). */
   readPreference?: ReadPreferenceLike;
+  /** @internal */
+  timeoutMS?: number;
 }
 
 /** @internal */
diff --git a/src/connection_string.ts b/src/connection_string.ts
index c22f54444b..c2abf08aaa 100644
--- a/src/connection_string.ts
+++ b/src/connection_string.ts
@@ -1108,9 +1108,6 @@ export const OPTIONS = {
   timeoutMS: {
     type: 'uint'
   },
-  defaultTimeoutMS: {
-    type: 'uint'
-  },
   tls: {
     type: 'boolean'
   },
diff --git a/src/db.ts b/src/db.ts
index c52d979eef..a3269a58e0 100644
--- a/src/db.ts
+++ b/src/db.ts
@@ -7,7 +7,7 @@ import { AggregationCursor } from './cursor/aggregation_cursor';
 import { ListCollectionsCursor } from './cursor/list_collections_cursor';
 import { RunCommandCursor, type RunCursorCommandOptions } from './cursor/run_command_cursor';
 import { MongoInvalidArgumentError } from './error';
-import type { MongoClient, MongoClientOptions, PkFactory } from './mongo_client';
+import type { MongoClient, PkFactory } from './mongo_client';
 import type { TODO_NODE_3286 } from './mongo_types';
 import type { AggregateOptions } from './operations/aggregate';
 import { CollectionsOperation } from './operations/collections';
@@ -67,8 +67,7 @@ const DB_OPTIONS_ALLOW_LIST = [
   'promoteValues',
   'compression',
   'retryWrites',
-  'timeoutMS',
-  'defaultTimeoutMS'
+  'timeoutMS'
 ];
 
 /** @internal */
@@ -83,10 +82,7 @@ export interface DbPrivate {
 }
 
 /** @public */
-export interface DbOptions
-  extends BSONSerializeOptions,
-    WriteConcernOptions,
-    Pick<MongoClientOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
+export interface DbOptions extends BSONSerializeOptions, WriteConcernOptions {
   /** If the database authentication is dependent on another databaseName. */
   authSource?: string;
   /** Force server to assign _id values instead of driver. */
@@ -99,6 +95,8 @@ export interface DbOptions
   readConcern?: ReadConcern;
   /** Should retry failed writes */
   retryWrites?: boolean;
+  /** @internal */
+  timeoutMS?: number;
 }
 
 /**
diff --git a/src/gridfs/download.ts b/src/gridfs/download.ts
index 8e8ca673f6..19c1e53b89 100644
--- a/src/gridfs/download.ts
+++ b/src/gridfs/download.ts
@@ -13,12 +13,10 @@ import type { FindOptions } from '../operations/find';
 import type { ReadPreference } from '../read_preference';
 import type { Sort } from '../sort';
 import type { Callback } from '../utils';
-import { type GridFSBucketOptions } from '.';
 import type { GridFSChunk } from './upload';
 
 /** @public */
-export interface GridFSBucketReadStreamOptions
-  extends Pick<GridFSBucketOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
+export interface GridFSBucketReadStreamOptions {
   sort?: Sort;
   skip?: number;
   /**
@@ -30,6 +28,8 @@ export interface GridFSBucketReadStreamOptions
    * to be returned by the stream. `end` is non-inclusive
    */
   end?: number;
+  /** @internal */
+  timeoutMS?: number;
 }
 
 /** @public */
diff --git a/src/gridfs/index.ts b/src/gridfs/index.ts
index 95cf43db55..f89428f5e2 100644
--- a/src/gridfs/index.ts
+++ b/src/gridfs/index.ts
@@ -3,7 +3,6 @@ import type { Collection } from '../collection';
 import type { FindCursor } from '../cursor/find_cursor';
 import type { Db } from '../db';
 import { MongoRuntimeError } from '../error';
-import { type MongoClientOptions } from '../mongo_client';
 import { type Filter, TypedEventEmitter } from '../mongo_types';
 import type { ReadPreference } from '../read_preference';
 import type { Sort } from '../sort';
@@ -30,15 +29,15 @@ const DEFAULT_GRIDFS_BUCKET_OPTIONS: {
 };
 
 /** @public */
-export interface GridFSBucketOptions
-  extends WriteConcernOptions,
-    Pick<MongoClientOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
+export interface GridFSBucketOptions extends WriteConcernOptions {
   /** The 'files' and 'chunks' collections will be prefixed with the bucket name followed by a dot. */
   bucketName?: string;
   /** Number of bytes stored in each chunk. Defaults to 255KB */
   chunkSizeBytes?: number;
   /** Read preference to be passed to read operations */
   readPreference?: ReadPreference;
+  /** @internal */
+  timeoutMS?: number;
 }
 
 /** @internal */
diff --git a/src/gridfs/upload.ts b/src/gridfs/upload.ts
index 9c013bfd0b..3f5559301f 100644
--- a/src/gridfs/upload.ts
+++ b/src/gridfs/upload.ts
@@ -8,7 +8,7 @@ import { type Callback, squashError } from '../utils';
 import type { WriteConcernOptions } from '../write_concern';
 import { WriteConcern } from './../write_concern';
 import type { GridFSFile } from './download';
-import type { GridFSBucket, GridFSBucketOptions } from './index';
+import type { GridFSBucket } from './index';
 
 /** @public */
 export interface GridFSChunk {
@@ -19,9 +19,7 @@ export interface GridFSChunk {
 }
 
 /** @public */
-export interface GridFSBucketWriteStreamOptions
-  extends WriteConcernOptions,
-    Pick<GridFSBucketOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
+export interface GridFSBucketWriteStreamOptions extends WriteConcernOptions {
   /** Overwrite this bucket's chunkSizeBytes for this file */
   chunkSizeBytes?: number;
   /** Custom file id for the GridFS file. */
@@ -38,6 +36,8 @@ export interface GridFSBucketWriteStreamOptions
    * @deprecated Will be removed in the next major version. Add an aliases field to the metadata document instead.
    */
   aliases?: string[];
+  /** @internal */
+  timeoutMS?: number;
 }
 
 /**
diff --git a/src/mongo_client.ts b/src/mongo_client.ts
index 61dfeb35ee..df64543f33 100644
--- a/src/mongo_client.ts
+++ b/src/mongo_client.ts
@@ -2,7 +2,7 @@ import { promises as fs } from 'fs';
 import type { TcpNetConnectOpts } from 'net';
 import type { ConnectionOptions as TLSConnectionOptions, TLSSocketOptions } from 'tls';
 
-import { type BSONSerializeOptions, type Document, type Long, resolveBSONOptions } from './bson';
+import { type BSONSerializeOptions, type Document, resolveBSONOptions } from './bson';
 import { ChangeStream, type ChangeStreamDocument, type ChangeStreamOptions } from './change_stream';
 import type { AutoEncrypter, AutoEncryptionOptions } from './client-side-encryption/auto_encrypter';
 import {
@@ -121,9 +121,7 @@ export interface MongoClientOptions extends BSONSerializeOptions, SupportedNodeC
   /** Specifies the name of the replica set, if the mongod is a member of a replica set. */
   replicaSet?: string;
   /** @internal This option is in development and currently has no behaviour. */
-  timeoutMS?: number | bigint | Long;
-  /** @internal This option is in development and currently has no behaviour. */
-  defaultTimeoutMS?: number | bigint | Long;
+  timeoutMS?: number;
   /** Enables or disables TLS/SSL for the connection. */
   tls?: boolean;
   /** A boolean to enable or disables TLS/SSL for the connection. (The ssl option is equivalent to the tls option.) */
@@ -805,8 +803,6 @@ export interface MongoOptions
         | 'socketTimeoutMS'
         | 'srvMaxHosts'
         | 'srvServiceName'
-        | 'timeoutMS'
-        | 'defaultTimeoutMS'
         | 'tlsAllowInvalidCertificates'
         | 'tlsAllowInvalidHostnames'
         | 'tlsInsecure'
@@ -901,4 +897,6 @@ export interface MongoOptions
    * TODO: NODE-5671 - remove internal flag
    */
   mongodbLogPath?: 'stderr' | 'stdout' | MongoDBLogWritable;
+  /** @internal */
+  timeoutMS?: number;
 }
diff --git a/src/operations/operation.ts b/src/operations/operation.ts
index fb31665097..8e4a22b547 100644
--- a/src/operations/operation.ts
+++ b/src/operations/operation.ts
@@ -1,5 +1,4 @@
 import { type BSONSerializeOptions, type Document, resolveBSONOptions } from '../bson';
-import { type MongoClientOptions } from '../mongo_client';
 import { ReadPreference, type ReadPreferenceLike } from '../read_preference';
 import type { Server } from '../sdam/server';
 import type { ClientSession } from '../sessions';
@@ -24,9 +23,7 @@ export interface OperationConstructor extends Function {
 }
 
 /** @public */
-export interface OperationOptions
-  extends BSONSerializeOptions,
-    Pick<MongoClientOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
+export interface OperationOptions extends BSONSerializeOptions {
   /** Specify ClientSession for this command */
   session?: ClientSession;
   willRetryWrite?: boolean;
@@ -37,6 +34,9 @@ export interface OperationOptions
   /** @internal Hints to `executeOperation` that this operation should not unpin on an ended transaction */
   bypassPinningCheck?: boolean;
   omitReadPreference?: boolean;
+
+  /** @internal */
+  timeoutMS?: number;
 }
 
 /** @internal */
diff --git a/src/sessions.ts b/src/sessions.ts
index 6c4e82b203..76951fcf84 100644
--- a/src/sessions.ts
+++ b/src/sessions.ts
@@ -23,7 +23,7 @@ import {
   MongoTransactionError,
   MongoWriteConcernError
 } from './error';
-import type { MongoClient, MongoClientOptions, MongoOptions } from './mongo_client';
+import type { MongoClient, MongoOptions } from './mongo_client';
 import { TypedEventEmitter } from './mongo_types';
 import { executeOperation } from './operations/execute_operation';
 import { RunAdminCommandOperation } from './operations/run_command';
@@ -53,14 +53,18 @@ import { WriteConcern } from './write_concern';
 const minWireVersionForShardedTransactions = 8;
 
 /** @public */
-export interface ClientSessionOptions
-  extends Pick<MongoClientOptions, 'timeoutMS' | 'defaultTimeoutMS'> {
+export interface ClientSessionOptions {
   /** Whether causal consistency should be enabled on this session */
   causalConsistency?: boolean;
   /** Whether all read operations should be read from the same snapshot for this session (NOTE: not compatible with `causalConsistency=true`) */
   snapshot?: boolean;
   /** The default TransactionOptions to use for transactions started on this session. */
   defaultTransactionOptions?: TransactionOptions;
+  /** @internal */
+  timeoutMS?: number;
+  /** @internal
+   * The value of timeoutMS used for CSOT. Used to override client timeoutMS */
+  defaultTimeoutMS?: number;
 
   /** @internal */
   owner?: symbol | AbstractCursor;
@@ -169,6 +173,8 @@ export class ClientSession extends TypedEventEmitter<ClientSessionEvents> {
       }
     }
 
+    options.timeoutMS ??= options.defaultTimeoutMS ?? client.options.timeoutMS;
+
     this.client = client;
     this.sessionPool = sessionPool;
     this.hasEnded = false;

From eb3757501c0ebd2b078c79c257b02f496371da11 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Thu, 4 Apr 2024 17:34:59 -0400
Subject: [PATCH 16/25] access timeoutMS optionally

---
 src/sessions.ts | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/sessions.ts b/src/sessions.ts
index 76951fcf84..79b03da2d3 100644
--- a/src/sessions.ts
+++ b/src/sessions.ts
@@ -135,6 +135,8 @@ export class ClientSession extends TypedEventEmitter<ClientSessionEvents> {
   [kPinnedConnection]?: Connection;
   /** @internal */
   [kTxnNumberIncrement]: number;
+  /** @internal */
+  timeoutMS?: number;
 
   /**
    * Create a client session.
@@ -173,12 +175,11 @@ export class ClientSession extends TypedEventEmitter<ClientSessionEvents> {
       }
     }
 
-    options.timeoutMS ??= options.defaultTimeoutMS ?? client.options.timeoutMS;
-
     this.client = client;
     this.sessionPool = sessionPool;
     this.hasEnded = false;
     this.clientOptions = clientOptions;
+    this.timeoutMS = options.defaultTimeoutMS ?? client.options?.timeoutMS;
 
     this.explicit = !!options.explicit;
     this[kServerSession] = this.explicit ? this.sessionPool.acquire() : null;

From 37c8ae2f590c59d00c9dd5ebe4e21c6f9068caa0 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Thu, 4 Apr 2024 17:35:28 -0400
Subject: [PATCH 17/25] migrate file to typescript and add additional tests

---
 .../{sessions.test.js => sessions.test.ts}    | 88 +++++++++++++++----
 1 file changed, 71 insertions(+), 17 deletions(-)
 rename test/unit/{sessions.test.js => sessions.test.ts} (90%)

diff --git a/test/unit/sessions.test.js b/test/unit/sessions.test.ts
similarity index 90%
rename from test/unit/sessions.test.js
rename to test/unit/sessions.test.ts
index ba58fef41e..f889ed9c6a 100644
--- a/test/unit/sessions.test.js
+++ b/test/unit/sessions.test.ts
@@ -1,21 +1,21 @@
-'use strict';
+import { expect } from 'chai';
+import * as sinon from 'sinon';
 
-const mock = require('../tools/mongodb-mock/index');
-const { expect } = require('chai');
-const { genClusterTime } = require('../tools/common');
-const {
-  ServerSessionPool,
-  ServerSession,
-  ClientSession,
+import {
   applySession,
-  BSON
-} = require('../mongodb');
-const { now, isHello } = require('../mongodb');
-const { getSymbolFrom } = require('../tools/utils');
-const { Long } = require('../mongodb');
-const { MongoRuntimeError } = require('../mongodb');
-const sinon = require('sinon');
-const { MongoClient } = require('../mongodb');
+  BSON,
+  ClientSession,
+  isHello,
+  Long,
+  MongoClient,
+  MongoRuntimeError,
+  now,
+  ServerSession,
+  ServerSessionPool
+} from '../mongodb';
+import { genClusterTime } from '../tools/common';
+import * as mock from '../tools/mongodb-mock/index';
+import { getSymbolFrom } from '../tools/utils';
 
 describe('Sessions - unit', function () {
   let client;
@@ -272,6 +272,60 @@ describe('Sessions - unit', function () {
         const txnNumberIncrementSymbol = getSymbolFrom(session, 'txnNumberIncrement');
         expect(session).to.have.property(txnNumberIncrementSymbol, 0);
       });
+
+      describe('defaultTimeoutMS', function () {
+        let client: MongoClient;
+        let session: ClientSession;
+        let server;
+
+        beforeEach(async () => {
+          server = await mock.createServer();
+        });
+
+        afterEach(async () => {
+          await mock.cleanup();
+        });
+
+        context('when client has defined timeoutMS', function () {
+          beforeEach(async () => {
+            client = new MongoClient(`mongodb://${server.hostAddress()}`, { timeoutMS: 100 });
+          });
+
+          context('when defaultTimeoutMS is defined', function () {
+            it(`overrides client's timeoutMS value`, function () {
+              session = new ClientSession(client, serverSessionPool, { defaultTimeoutMS: 200 });
+              expect(session).to.have.property('timeoutMS', 200);
+            });
+          });
+
+          context('when defaultTimeoutMS is not defined', function () {
+            it(`inherits client's timeoutMS value`, function () {
+              session = new ClientSession(client, serverSessionPool, {});
+              expect(session).to.have.property('timeoutMS', 100);
+            });
+          });
+        });
+
+        context('when client has not defined timeoutMS', function () {
+          beforeEach(async () => {
+            client = new MongoClient(`mongodb://${server.hostAddress()}`, {});
+          });
+
+          context('when defaultTimeoutMS is defined', function () {
+            it(`sets timeoutMS to defaultTimeoutMS`, function () {
+              session = new ClientSession(client, serverSessionPool, { defaultTimeoutMS: 200 });
+              expect(session).to.have.property('timeoutMS', 200);
+            });
+          });
+
+          context('when defaultTimeoutMS is not defined', function () {
+            it(`leaves timeoutMS as undefined`, function () {
+              session = new ClientSession(client, serverSessionPool, {});
+              expect(session.timeoutMS).to.be.undefined;
+            });
+          });
+        });
+      });
     });
 
     describe('get serverSession()', () => {
@@ -442,7 +496,7 @@ describe('Sessions - unit', function () {
     beforeEach(async () => {
       server = await mock.createServer();
       server.setMessageHandler(request => {
-        var doc = request.document;
+        const doc = request.document;
         if (isHello(doc)) {
           request.reply(Object.assign({}, mock.HELLO, { logicalSessionTimeoutMinutes: 10 }));
         }

From b860acca8c4cb59a7802d45da7339eb0b83b4714 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Fri, 5 Apr 2024 13:56:48 -0400
Subject: [PATCH 18/25] add inheritance tests

---
 .../node_csot.test.ts                         | 96 ++++++++++++++++++-
 1 file changed, 94 insertions(+), 2 deletions(-)

diff --git a/test/integration/client-side-operations-timeout/node_csot.test.ts b/test/integration/client-side-operations-timeout/node_csot.test.ts
index 06e8179daf..a187c10a2d 100644
--- a/test/integration/client-side-operations-timeout/node_csot.test.ts
+++ b/test/integration/client-side-operations-timeout/node_csot.test.ts
@@ -1,4 +1,96 @@
-/* eslint-disable @typescript-eslint/no-empty-function */
 /* Anything javascript specific relating to timeouts */
+import { expect } from 'chai';
+import * as sinon from 'sinon';
 
-describe.skip('CSOT driver tests', () => {});
+import {
+  type ClientSession,
+  type Collection,
+  type Db,
+  type FindCursor,
+  type MongoClient
+} from '../../mongodb';
+
+describe('CSOT driver tests', () => {
+  afterEach(() => {
+    sinon.restore();
+  });
+
+  describe('timeoutMS inheritance', () => {
+    let client: MongoClient;
+    let db: Db;
+    let coll: Collection;
+
+    beforeEach(async function () {
+      client = this.configuration.newClient(undefined, { timeoutMS: 100 });
+      db = client.db('test', { timeoutMS: 200 });
+    });
+
+    afterEach(async () => {
+      if (client) await client.close();
+    });
+
+    describe('when timeoutMS is provided on an operation', () => {
+      beforeEach(() => {
+        coll = db.collection('test', { timeoutMS: 300 });
+      });
+
+      describe('when in a session', () => {
+        let cursor: FindCursor;
+        let session: ClientSession;
+
+        beforeEach(() => {
+          session = client.startSession({ defaultTimeoutMS: 400 });
+          cursor = coll.find({}, { session, timeoutMS: 500 });
+        });
+
+        afterEach(async () => {
+          await cursor.close();
+          await session.endSession();
+        });
+
+        it('overrides the value provided on the db and the session', async () => {
+          expect(cursor.cursorOptions).to.have.property('timeoutMS', 500);
+        });
+      });
+
+      describe('when not in a session', () => {
+        let cursor: FindCursor;
+
+        beforeEach(() => {
+          db = client.db('test', { timeoutMS: 200 });
+          coll = db.collection('test', { timeoutMS: 300 });
+          cursor = coll.find({}, { timeoutMS: 400 });
+        });
+
+        afterEach(async () => {
+          await cursor.close();
+        });
+
+        it('overrides the value provided on the db', async () => {
+          expect(cursor.cursorOptions).to.have.property('timeoutMS', 400);
+        });
+      });
+    });
+
+    describe('when timeoutMS is provided on a collection', () => {
+      beforeEach(() => {
+        db = client.db('test', { timeoutMS: 200 });
+        coll = db.collection('test', { timeoutMS: 300 });
+      });
+
+      it('overrides the value provided on the db', () => {
+        expect(coll.s.options).to.have.property('timeoutMS', 300);
+      });
+
+      describe('when timeoutMS is provided on a db', () => {
+        beforeEach(() => {
+          db = client.db('test', { timeoutMS: 200 });
+        });
+
+        it('overrides the value provided on the client', () => {
+          expect(db.s.options).to.have.property('timeoutMS', 200);
+        });
+      });
+    });
+  });
+});

From fec996cbf83003364e4b5ddc9b0cf156102c34b0 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Fri, 5 Apr 2024 14:13:12 -0400
Subject: [PATCH 19/25] remove field from options

---
 src/sessions.ts | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/sessions.ts b/src/sessions.ts
index 79b03da2d3..a5acf2aed6 100644
--- a/src/sessions.ts
+++ b/src/sessions.ts
@@ -60,8 +60,6 @@ export interface ClientSessionOptions {
   snapshot?: boolean;
   /** The default TransactionOptions to use for transactions started on this session. */
   defaultTransactionOptions?: TransactionOptions;
-  /** @internal */
-  timeoutMS?: number;
   /** @internal
    * The value of timeoutMS used for CSOT. Used to override client timeoutMS */
   defaultTimeoutMS?: number;

From a7cff11da4f89d6d81e0e99ae4f3ebe036c5374a Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Fri, 5 Apr 2024 14:46:28 -0400
Subject: [PATCH 20/25] add error logich when timeoutMS is specified on
 explicit session and at operation level

---
 src/operations/operation.ts | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/operations/operation.ts b/src/operations/operation.ts
index 8e4a22b547..921db13db0 100644
--- a/src/operations/operation.ts
+++ b/src/operations/operation.ts
@@ -1,4 +1,5 @@
 import { type BSONSerializeOptions, type Document, resolveBSONOptions } from '../bson';
+import { MongoInvalidArgumentError } from '../error';
 import { ReadPreference, type ReadPreferenceLike } from '../read_preference';
 import type { Server } from '../sdam/server';
 import type { ClientSession } from '../sessions';
@@ -35,7 +36,7 @@ export interface OperationOptions extends BSONSerializeOptions {
   bypassPinningCheck?: boolean;
   omitReadPreference?: boolean;
 
-  /** @internal */
+  /** @internal TODO(NODE-5688): make this public */
   timeoutMS?: number;
 }
 
@@ -72,6 +73,11 @@ export abstract class AbstractOperation<TResult = any> {
     this.bsonOptions = resolveBSONOptions(options);
 
     this[kSession] = options.session != null ? options.session : undefined;
+    if (options?.session?.explicit && options?.session?.timeoutMS != null && options.timeoutMS) {
+      throw new MongoInvalidArgumentError(
+        'Do not specify timeoutMS on operation if already specified on an explicit session'
+      );
+    }
 
     this.options = options;
     this.bypassPinningCheck = !!options.bypassPinningCheck;

From d34ae2f8a1e6c22b11f508dc2e0dcffc8e4232cc Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Fri, 5 Apr 2024 14:46:37 -0400
Subject: [PATCH 21/25] Add todo comments

---
 src/collection.ts             | 2 +-
 src/cursor/abstract_cursor.ts | 3 +++
 src/db.ts                     | 2 +-
 src/gridfs/download.ts        | 2 +-
 src/gridfs/index.ts           | 2 +-
 src/gridfs/upload.ts          | 2 +-
 src/mongo_client.ts           | 4 ++--
 7 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/collection.ts b/src/collection.ts
index 180e9822e8..3665498995 100644
--- a/src/collection.ts
+++ b/src/collection.ts
@@ -106,7 +106,7 @@ export interface CollectionOptions extends BSONSerializeOptions, WriteConcernOpt
   readConcern?: ReadConcernLike;
   /** The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST). */
   readPreference?: ReadPreferenceLike;
-  /** @internal */
+  /** @internal TODO(NODE-5688): make this public */
   timeoutMS?: number;
 }
 
diff --git a/src/cursor/abstract_cursor.ts b/src/cursor/abstract_cursor.ts
index 51cf4ce700..10aa5eea5f 100644
--- a/src/cursor/abstract_cursor.ts
+++ b/src/cursor/abstract_cursor.ts
@@ -109,6 +109,8 @@ export interface AbstractCursorOptions extends BSONSerializeOptions {
    */
   awaitData?: boolean;
   noCursorTimeout?: boolean;
+  /** @internal TODO(NODE-5688): make this public */
+  timeoutMS?: number;
 }
 
 /** @internal */
@@ -184,6 +186,7 @@ export abstract class AbstractCursor<
           : ReadPreference.primary,
       ...pluckBSONSerializeOptions(options)
     };
+    this[kOptions].timeoutMS = options.timeoutMS;
 
     const readConcern = ReadConcern.fromOptions(options);
     if (readConcern) {
diff --git a/src/db.ts b/src/db.ts
index a3269a58e0..423979a0d4 100644
--- a/src/db.ts
+++ b/src/db.ts
@@ -95,7 +95,7 @@ export interface DbOptions extends BSONSerializeOptions, WriteConcernOptions {
   readConcern?: ReadConcern;
   /** Should retry failed writes */
   retryWrites?: boolean;
-  /** @internal */
+  /** @internal TODO(NODE-5688): make this public */
   timeoutMS?: number;
 }
 
diff --git a/src/gridfs/download.ts b/src/gridfs/download.ts
index 19c1e53b89..6b0fc57fc6 100644
--- a/src/gridfs/download.ts
+++ b/src/gridfs/download.ts
@@ -28,7 +28,7 @@ export interface GridFSBucketReadStreamOptions {
    * to be returned by the stream. `end` is non-inclusive
    */
   end?: number;
-  /** @internal */
+  /** @internal TODO(NODE-5688): make this public */
   timeoutMS?: number;
 }
 
diff --git a/src/gridfs/index.ts b/src/gridfs/index.ts
index f89428f5e2..51c32b7a01 100644
--- a/src/gridfs/index.ts
+++ b/src/gridfs/index.ts
@@ -36,7 +36,7 @@ export interface GridFSBucketOptions extends WriteConcernOptions {
   chunkSizeBytes?: number;
   /** Read preference to be passed to read operations */
   readPreference?: ReadPreference;
-  /** @internal */
+  /** @internal TODO(NODE-5688): make this public */
   timeoutMS?: number;
 }
 
diff --git a/src/gridfs/upload.ts b/src/gridfs/upload.ts
index 3f5559301f..12440f2670 100644
--- a/src/gridfs/upload.ts
+++ b/src/gridfs/upload.ts
@@ -36,7 +36,7 @@ export interface GridFSBucketWriteStreamOptions extends WriteConcernOptions {
    * @deprecated Will be removed in the next major version. Add an aliases field to the metadata document instead.
    */
   aliases?: string[];
-  /** @internal */
+  /** @internal TODO(NODE-5688): make this public */
   timeoutMS?: number;
 }
 
diff --git a/src/mongo_client.ts b/src/mongo_client.ts
index df64543f33..1e21aefe35 100644
--- a/src/mongo_client.ts
+++ b/src/mongo_client.ts
@@ -120,7 +120,7 @@ export type SupportedNodeConnectionOptions = SupportedTLSConnectionOptions &
 export interface MongoClientOptions extends BSONSerializeOptions, SupportedNodeConnectionOptions {
   /** Specifies the name of the replica set, if the mongod is a member of a replica set. */
   replicaSet?: string;
-  /** @internal This option is in development and currently has no behaviour. */
+  /** @internal TODO(NODE-5688): This option is in development and currently has no behaviour.  */
   timeoutMS?: number;
   /** Enables or disables TLS/SSL for the connection. */
   tls?: boolean;
@@ -897,6 +897,6 @@ export interface MongoOptions
    * TODO: NODE-5671 - remove internal flag
    */
   mongodbLogPath?: 'stderr' | 'stdout' | MongoDBLogWritable;
-  /** @internal */
+  /** @internal TODO(NODE-5688): make this public */
   timeoutMS?: number;
 }

From d8f97a2093340730b35223266cf1bb3296b65211 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Fri, 5 Apr 2024 14:46:45 -0400
Subject: [PATCH 22/25] add csot tests

---
 .../client-side-operations-timeout/node_csot.test.ts            | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/integration/client-side-operations-timeout/node_csot.test.ts b/test/integration/client-side-operations-timeout/node_csot.test.ts
index a187c10a2d..4b1b0558b7 100644
--- a/test/integration/client-side-operations-timeout/node_csot.test.ts
+++ b/test/integration/client-side-operations-timeout/node_csot.test.ts
@@ -48,7 +48,7 @@ describe('CSOT driver tests', () => {
           await session.endSession();
         });
 
-        it('overrides the value provided on the db and the session', async () => {
+        it('throws an error', async () => {
           expect(cursor.cursorOptions).to.have.property('timeoutMS', 500);
         });
       });

From 11f26e18643b3c5f23ff0260a3c17a3cbbad00a6 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Fri, 5 Apr 2024 14:57:39 -0400
Subject: [PATCH 23/25] revert duplicated tests

---
 test/unit/connection_string.test.ts | 51 -----------------------------
 1 file changed, 51 deletions(-)

diff --git a/test/unit/connection_string.test.ts b/test/unit/connection_string.test.ts
index ab4b827d7a..2a38fc491a 100644
--- a/test/unit/connection_string.test.ts
+++ b/test/unit/connection_string.test.ts
@@ -14,7 +14,6 @@ import {
   DOCUMENT_DB_MSG,
   FEATURE_FLAGS,
   type Log,
-  Long,
   MongoAPIError,
   MongoClient,
   MongoCredentials,
@@ -923,56 +922,6 @@ describe('Connection String', function () {
     });
   });
 
-  describe('when timeoutMS is provided as a client option', function () {
-    const connString = 'mongodb://host';
-    const types = ['number', 'bigint', 'Long'];
-    const values = [-100, 0, 100];
-
-    for (const type of types) {
-      describe(`when timeoutMS provided as a ${type}`, function () {
-        for (const v of values) {
-          const timeoutMS =
-            type === 'number' ? v : type === 'bigint' ? BigInt(v) : Long.fromNumber(v);
-          describe(`when timeoutMS is ${
-            v < 0 ? 'negative' : v > 0 ? 'positive' : 'zero'
-          }`, function () {
-            if (v >= 0) {
-              it('sets the value correctly as a number', function () {
-                const options = parseOptions(connString, { timeoutMS });
-                expect(options.timeoutMS).to.equal(v);
-              });
-            } else {
-              it('throws MongoParseError', function () {
-                expect(() => parseOptions(connString, { timeoutMS })).to.throw(MongoParseError);
-              });
-            }
-          });
-        }
-      });
-    }
-  });
-
-  describe('when timeoutMS is provided in the connection string', function () {
-    const values = [-100, 0, 100];
-    for (const v of values) {
-      const connString = `mongodb://host?timeoutMS=${v}`;
-      describe(`when timeoutMS is ${
-        v < 0 ? 'negative' : v > 0 ? 'positive' : 'zero'
-      }`, function () {
-        if (v >= 0) {
-          it('sets the value correctly as a number', function () {
-            const options = parseOptions(connString);
-            expect(options.timeoutMS).to.equal(v);
-          });
-        } else {
-          it('throws MongoParseError', function () {
-            expect(() => parseOptions(connString)).to.throw(MongoParseError);
-          });
-        }
-      });
-    }
-  });
-
   describe('non-genuine hosts', () => {
     beforeEach(() => {
       process.env.MONGODB_LOG_CLIENT = 'info';

From aa2a8bb5f7780110c0bdfeb42b3f2668f0d4d84d Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Mon, 8 Apr 2024 10:01:44 -0400
Subject: [PATCH 24/25] Apply suggestions from code review

Co-authored-by: Durran Jordan <durran@gmail.com>
---
 .../client-side-operations-timeout/node_csot.test.ts       | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/test/integration/client-side-operations-timeout/node_csot.test.ts b/test/integration/client-side-operations-timeout/node_csot.test.ts
index 4b1b0558b7..b6a936afbb 100644
--- a/test/integration/client-side-operations-timeout/node_csot.test.ts
+++ b/test/integration/client-side-operations-timeout/node_csot.test.ts
@@ -26,7 +26,7 @@ describe('CSOT driver tests', () => {
     });
 
     afterEach(async () => {
-      if (client) await client.close();
+      await client?.close();
     });
 
     describe('when timeoutMS is provided on an operation', () => {
@@ -44,7 +44,8 @@ describe('CSOT driver tests', () => {
         });
 
         afterEach(async () => {
-          await cursor.close();
+          await cursor?.close();
+          await session?.endSession();
           await session.endSession();
         });
 
@@ -63,7 +64,7 @@ describe('CSOT driver tests', () => {
         });
 
         afterEach(async () => {
-          await cursor.close();
+          await cursor?.close();
         });
 
         it('overrides the value provided on the db', async () => {

From 5ef3ac1b373d213a6f6fb8ca516b640acb834130 Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Tue, 9 Apr 2024 17:13:21 -0400
Subject: [PATCH 25/25] move session check logic to executeOperation

---
 src/operations/execute_operation.ts | 5 +++++
 src/operations/operation.ts         | 6 ------
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/operations/execute_operation.ts b/src/operations/execute_operation.ts
index 59f58f8748..b2951170ad 100644
--- a/src/operations/execute_operation.ts
+++ b/src/operations/execute_operation.ts
@@ -110,6 +110,11 @@ export async function executeOperation<
   } else if (session.client !== client) {
     throw new MongoInvalidArgumentError('ClientSession must be from the same MongoClient');
   }
+  if (session.explicit && session?.timeoutMS != null && operation.options.timeoutMS != null) {
+    throw new MongoInvalidArgumentError(
+      'Do not specify timeoutMS on operation if already specified on an explicit session'
+    );
+  }
 
   const readPreference = operation.readPreference ?? ReadPreference.primary;
   const inTransaction = !!session?.inTransaction();
diff --git a/src/operations/operation.ts b/src/operations/operation.ts
index 921db13db0..e71baa44a9 100644
--- a/src/operations/operation.ts
+++ b/src/operations/operation.ts
@@ -1,5 +1,4 @@
 import { type BSONSerializeOptions, type Document, resolveBSONOptions } from '../bson';
-import { MongoInvalidArgumentError } from '../error';
 import { ReadPreference, type ReadPreferenceLike } from '../read_preference';
 import type { Server } from '../sdam/server';
 import type { ClientSession } from '../sessions';
@@ -73,11 +72,6 @@ export abstract class AbstractOperation<TResult = any> {
     this.bsonOptions = resolveBSONOptions(options);
 
     this[kSession] = options.session != null ? options.session : undefined;
-    if (options?.session?.explicit && options?.session?.timeoutMS != null && options.timeoutMS) {
-      throw new MongoInvalidArgumentError(
-        'Do not specify timeoutMS on operation if already specified on an explicit session'
-      );
-    }
 
     this.options = options;
     this.bypassPinningCheck = !!options.bypassPinningCheck;